1. Field of the Invention
This invention relates to phenol/aldehyde-based polyols and to rigid cellular compositions derived from these polyols. Specifically it deals with modified benzylic ether-containing resole polyols and the rapid curing, low combustibility, low friability, closed cell, rigid cellular plastic compositions obtained by reaction of the polyols with polyisocyanates.
2. Description of the Prior Art
Our co-pending U.S. patent application, Ser. No. 458,283, which is incorporated herein by reference, distinguishes in detail between resoles, novolacs, and benzyl ether-containing resins--all of which are known in the prior art. Resoles, which are made with excess aldehyde (relative to phenol) under alkaline catalysis, have numerous hydroxymethyl substituents on the phenol rings. Novolacs, which are made with a molar excess of phenol (relative to aldehyde) under acid catalysts have no (or very few) hydroxymethyl substituents. Benzyl ether-containing resins (U.S. Pat. No. 3,485,797; Frazer, et al, Journal of Applied Chemistry, 7, 689 (1957) are obtained using certain metal salts as catalysts and can be made with (resole) or without (novolac) hydroxymethyl substituents, depending on the ratio of phenol and aldehyde.
Such prior art phenol/aldehyde condensates can be further polymerized (novolacs require added aldehyde) to phenolic foams which have excellent inherent flame retardancy but are opened cell and friable. The excellent inherent flame retardancy has motivated a desire to incorporate phenolic structure in rigid polyurethane foam.
Use of benzyl ether-containing resins as polyols in the preparation of rigid polyurethane foams, as disclosed in U.S. Pat. No. 3,948,824, results in foams which were slow to cure and friable. Desirable strength and friability properties could be achieved by post-curing the foams at elevated temperature (U.S. Pat. No. 4,293,658 and Schafer, et al, Journal of Cellular Plastics, 1978, 147). The latter requirement makes such systems unsuitable for processing on commonly available commercial foam equipment.